Members of the grasses, such as wheat, rice and maize, represent some of the major economically relevant crops. According to the Food and Agriculture Organization, the world production of grasses in 2008 was 2.5 billion metric tons (FAOSTAT: Food and Agriculture Organization of the United Nations, Rome Italy website). In addition to their nutritional importance, grasses have recently attracted attention as potential second generation bioenergy crops due to their potential to produce large quantities of biomass in short times with little agricultural input from growers (Heaton, E A, et al., Global Change Biology 14, 2000-14, 2008).
The grasses are noteworthy for their complex cell wall structure that is distinct from that of dicotyledons such as trees. One profound difference is that heteroxylans constitute the major hemicellulose in their primary cell wall. The cell walls of grasses also have less pectic polysaccharides compared to other higher plants. Another major difference in the primary cell wall is the presence of (1,3; 1,4)-β-D-glucans, a polysaccharide that is absent outside the Poales in higher plants. The unique cell wall structure of grasses such as maize has potential to provide large quantities sugars that can be used as feedstocks for the production of biofuels such as ethanol. For example, the glucose containing components of cell walls of maize can be used in the production of ethanol.
There is a need to develop plants, such as grasses, with improved cell wall characteristics such as increased levels of glucose containing polymers.